Yes, I'd book the later flight. If the change of planes in Atlanta is on the same airline, they should hold the connecting flight if there is a delay on your flight. Even though I dislike Atlanta, you can get from one concourse to the other in a short period of time. I would contact the airline and explain the situation. Then ask them if you booked the early flight what the penalty would be to get the later flight. Too bad there isn't one around 1:30, that would be just about perfect. Still, if it were me, I'd book the 2:40.